Final answer:
Keratinocytes in the epidermis produce the protein keratin, which hardens and waterproofs skin, hair, and nails. These cells move up through the epidermis and die, creating a protective layer. The epidermis also contains cells for pigment, immunity, and sensation but lacks nerves and blood vessels.
Step-by-step explanation:
The epidermis, an integral part of our skin, is composed mainly of epithelial cells called keratinocytes. These keratinocytes are responsible for producing a tough, fibrous protein known as keratin, which is pivotal for giving skin, hair, and nails their hardness and water-resistant properties. As these cells mature, they move upwards through the layers of the epidermis, progressively filling with keratin. By the time they reach the surface to form the stratum corneum, they are no longer alive. This outermost layer creates a protective, waterproof barrier that is continuously shed and replaced by new cells from the deeper epidermal layers.
Besides keratinocytes, the epidermis houses other cell types, such as melanocytes (pigment-producing cells), Langerhans cells (involved in immune response), and Merkel cells (sensory cells). The epidermis is devoid of any nerve endings or blood vessels and can vary in thickness, having an additional layer in areas experiencing greater friction, like the palms of hands and soles of feet.